The present invention relates generally to a fluid transfer machine, and more particularly to a fluid transfer machine that can be used as a pump or motor.
Fluid transfer machines can have different types of pumping mechanisms to move fluid through the machine. One type of pumping mechanism useful for a variety of fluid transfer machines is a positive displacement rotary pump. Conventional positive displacement rotary pumps include single rotors (vane, piston, progressing cavity, screw or peristaltic), or multiple rotors (internal/external gear, lobe, circumferential piston or screw). The mechanisms all have advantages and drawbacks, depending on the fluid to be pumped, and the particular application.
During movement of the pumping mechanisms, friction can cause wear and heating of the moving parts, which can degrade the machine over time, and lead to failure and/or costly and time-consuming repairs.
Fluid is typically used for lubricating the moving parts of the pumping mechanism. It is particularly advantageous to use a portion of the fluid being transferred through the machine as the cooling and lubricating fluid. It is well-known to provide additional flow passages through the housing of the machine and to tap or bleed off a portion of the fluid from the primary flow for use in lubrication and cooling. It is also known to intentionally provide leak paths between the moving components and then collect the fluid for return to the primary flow path. Examples of such machines are shown in Ishizuka, U.S. Pat. No. 6,048,185; Riddle, U.S. Pat. No. 3,994,634; and Zieg, U.S. Pat. No. 2,940,399.
It is also known to provide grooves in rotating shafts to assist in moving the cooling and lubrication fluid between the components in the fluid transfer machine, such as shown in Sluijters, U.S. Pat. No. 3,368,799.
While the machines shown and described above are useful in some applications, forming (e.g., drilling) the flow passages in the machine to direct the cooling and lubricating fluid to the various components can be labor-intensive and difficult. A number of angled passages are typically required, which requires multiple drilling steps. This is shown particularly in Janczak, U.S. Pat. No. 4,548,557, where complex passages requiring multiple drilling steps are used to avoid connecting the primary fluid flow path directly with the drive shaft. Janczak points out that high pressure fluid around the drive shaft could damage or weaken the seals along the shaft.
Providing such complex passages also increases the size of the machine and the space necessary for locating the machine in the fluid transfer system. With the demand for smaller and lighter pumps and motors, and smaller fluid transfer systems, it has become increasingly difficult to manufacture such machines in a cost-effective, compact manner, particularly for high-performance applications which require high flow rates.
One partial solution is shown in Dworak, U.S. Pat. No. 4,038,000, where the primary flow path through the machine is directed from the inlet, through the gear mechanism (stub shafts and bearings), to the outlet. There are no additional lubrication and cooling passages for the bearings and stub shafts, beyond what is used to direct the primary flow through the machine. The Dworak machine has the advantage in that the machine is smaller and easier to construct, and keeps the pumping mechanism properly lubricated and cooled. Nevertheless, the Dworak machine does not address friction and wearing of the drive shaft, as the primary flow path in Dworak is limited to only the stub shaft and associated bearings. The drive shaft is also rotating, and particularly in high-performance applications, also has friction and wear issues.
Thus, it is believed there is a further demand for an improved fluid transfer machine, particularly a machine that can be used as a pump or motor, where the drive shaft is properly lubricated and cooled, and which has a compact design that is easily-manufactured.
The present invention provides a novel and unique fluid transfer machine, particularly useful as a pump or motor, where the drive shaft (as well as the pump mechanism) is properly lubricated and cooled, and which has a compact design that is easily-manufactured.
According to the present invention, the fluid transfer machine has a pumping mechanism that is a positive displacement, rotary (single or multiple rotor) type pump appropriate for the particular application. An external gear-type pump is used in a preferred form of the invention. The machine can be run as a motor or as a pump, as should be well know, typically by reversing the rotation of the pumping mechanism.
The pumping mechanism includes a typical arrangement of components such as bearings and stub shafts, which are preferably lubricated in a conventional manner, such as by allowing a slight leak path between the moving components.
The pumping mechanism is driven by a drive shaft, which extends out of the housing and is acted upon by (or acts upon) an external device. To lubricate and cool the drive shaft, and in particular the portion of the drive shaft internal to the housing, the drive shaft is located in the primary flow path through the fluid transfer machine. In a preferred embodiment, the drive shaft is located in the inlet flow path of the primary flow. The primary flow is directed from the inlet port to a cavity that surrounds the drive shaft, at a location between a pair of journal bearings or sleeves. The flow then continues to the suction side of the pumping mechanism. Alternatively, the drive shaft could be located in the outlet flow path of the primary flow path, between the pressure side of the pumping mechanism and the outlet port. In either case, the primary flow cools and lubricates the drive shaft (and drive shaft bearings), and reduces the size of the fluid transfer machine, as additional cooling and lubrication flow passage(s) are not necessary. This also reduces the complexity of manufacture of the machine.
The present invention thereby addresses many of the issues with prior machines, and provides a fluid transfer machine, particularly useful as a pump or motor, where the drive shaft (as well as the pump mechanism) is lubricated and cooled, and which has a compact design that is easily-manufactured.